THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP00/04268. The present invention relates to a magnetic head suitable for recording/reproducing of great amounts of magnetic information on a magnetic recording medium, and further relates to a sealing glass for joining a pair of magnetic core halves configuring such a magnetic head.
The present invention relates to a magnetic head suitable for recording/reproducing of great amounts of magnetic information on a magnetic recording medium, and further relates to a sealing glass for joining a pair of magnetic core halves configuring such a magnetic head.
In recent years, magnetic recording media with a high coercive force have been used with decreasing size and increasing capacity of a magnetic recording/reproducing apparatus. The development of a magnetic head for high-density magnetic recording, having a capability of sufficiently writing signals on such a medium, has been demanded strongly. The magnetic head is designed so as to be capable of being used for a high-capacity magnetic recording medium by using a magnetic material having a high value of saturation magnetic flux density as a core and by decreasing a gap length. For example, for this purpose, there has been proposed a Metal-in-Gap (MIG) head in which the gap facing surfaces of magnetic core halves are coated with a magnetic substance with a high saturation magnetic flux density (for example, Fexe2x80x94Taxe2x80x94N, Fexe2x80x94Nbxe2x80x94N, Fexe2x80x94Nbxe2x80x94Sixe2x80x94Bxe2x80x94N, Coxe2x80x94Taxe2x80x94Zrxe2x80x94Nb, or Coxe2x80x94Nbxe2x80x94Zrxe2x80x94N, hereinafter abbreviated as a magnetic substance) in a thin film shape.
FIG. 2 shows a construction of an MIG head. Metallic ferromagnetic films 3 and 4 with a high saturation magnetic flux density are formed on the magnetic gap facing surfaces of magnetic core halves 1 and 2 made of ferrite, and the magnetic gap facing surfaces are butted together via a magnetic gap material 5 and are fixed to each other by sealing glasses 6 and 7.
The MIG head is manufactured by a process shown in FIG. 3 on the whole. First, a coil groove 10 and glass grooves 11 are formed in a pair of ferrite cores (a). Then, track grooves 12 for regulating track width are formed (b). Further, metallic ferromagnetic films 3 and 4 (not shown) are formed on magnetic gap facing surfaces having been ground, and a film of a magnetic gap material 5 (not shown) is formed on the metallic ferromagnetic film 3, 4. Next, the magnetic gap facing surfaces are butted together and a front sealing glass 6 and. a back sealing glass 7 are disposed (c), and thereafter the paired core halves are joined to each other by heat treatment (d). Thus, a magnetic core block in which sealing glasses are molded to join the ferrite cores is cut to a predetermined thickness and ground, by which a magnetic head chip 13 is manufactured (e). This magnetic head chip is subjected to treatment such as base bonding and wire coiling, thereby completing a magnetic head.
When the sealing glasses 6 and 7 are molded, the operation must be performed usually at about 500xc2x0 C. to prevent the magnetic characteristics of magnetic film from being impaired. The back sealing glass 7 on the back gap side is filled by heating and softening glass and pouring it, by using sealing glass whose working point is about 500xc2x0 C. The proper working point of the back sealing glass is 490 to 520xc2x0 C. The working point is defined as a. temperature at which the viscosity of glass is about 103 Paxc2x7s. Also, in order to reduce the occurrence of cracks of magnetic head caused by distortion or other faults and to manufacture magnetic heads in high yields, the coefficient of thermal expansion of the back sealing glass should preferably be (75 to 100)xc3x9710xe2x88x927xc2x0 C.xe2x88x921 (for example, Japanese Patent Application Laid-Open No. 8-180310).
On the other hand, the front sealing glass 6 for joining the front gap side is filled by being pushed in from the front gap side at a heating temperature of about 500xc2x0 C. while a pressure is applied to the glass, by using a sealing glass having a working point higher than 500xc2x0 C. The reason for this is that if the front sealing glass 6 is filled by pouring glass having a low working point, since low-viscosity glass is liable to react with magnetic film, gap collapse or air bubble is produced, so that the magnetic characteristics are deteriorated. Therefore, using glass having a working point slightly higher than the heating temperature, contrivance is made to reduce the reaction by pushing in the glass while applying a pressure in a state of high viscosity. At this time, the working point of the front sealing glass should preferably be 540 to 560xc2x0 C. Also, from the viewpoint of output characteristics of magnetic head, in order to produce a proper distortion on the magnetic substance, the coefficient of thermal expansion of the front sealing glass should preferably be (80 to 95)xc3x9710xe2x88x927xc2x0 C.xe2x88x921 (for example, Japanese Patent Application Laid-Open No. 7-161011).
As sealing glass for magnetic head that meets the above condition, for the sealing glass on the front gap side, glass having a composition of 6 to 17 wt % SiO2, 7 to 16 wt % B2O3, 60 to 77 wt % PbO, 0 to 13 wt % ZnO, 0 to 2 wt % Al2O3, 0 to 1 wt % K2O, 0 to 3 wt % Na2O, 0 to 5 wt % La2O3, and 0 to 5 wt % BaO on an oxide basis has so far been used, and for the sealing glass on the back gap side, glass having a composition of 1 to 6 wt % SiO2, 7 to 10 wt % B2O3, 60 to 78 wt % PbO, 10 to 25 wt % ZnO, 0 to 3 wt % Al2O3, 0 to 8 wt % of ZrO2, and 0 to 3 wt % BaO on an oxide basis has so far been used (for example, Japanese Patent Application Laid-Open Nos. 7-161011 and 8-180310).
As described above, since a high impact is given during cutting and grinding operations in the manufacturing process for magnetic head, cracks sometimes occur in the sealing glass, which has a relatively lower strength than any material constituting the magnetic head, which finally causes cracks in the magnetic head. Therefore, the front and back sealing glasses are required to have a high strength.
Further, in recent years, in order to increase the density of magnetic recording on a medium, a magnetic head having a narrower track width and a shorter gap length than before has been demanded. As a manufacturing method for obtaining a magnetic head having a narrow track width and a short gap length with high accuracy, a method has been proposed in which a pair of magnetic core halves are butted together, and are first fixed by only a back sealing glass, and then a front sealing glass is molded after a track width on the front gap side is regulated (for example, Japanese Patent Application Laid-Open Nb. 7-220218).
FIG. 4 shows the outline of the manufacturing process. As is shown in FIG. 3, the coil groove 10 and the glass grooves 11 and the track grooves 12 are formed in a pair of ferrite core halves, and the metallic ferromagnetic films 3 and 4 (not shown) and the film of the magnetic gap material 5 (not shown) are formed on the magnetic gap facing surfaces having been ground. Then, the back sealing glass 7 is disposed on the butted paired core halves (c), and after heating, the back gap side is first joined. The nearby portion of a magnetic core block having been made in unit form is fabricated to regulate a track width of the butted portion on the front gap side. Thereafter, the front sealing glass 6 is disposed (d), and the front gap side is filled by reheating (e). The magnetic core block is cut and ground, by which the magnetic head chip 13 is manufactured. This magnetic head chip is subjected to treatment such as base bonding and wire coiling, thereby completing a magnetic head. By this manufacturing method, a magnetic head with a high-accuracy narrow track width without track shift and a stable gap length accuracy can be obtained.
However, for general glass materials, crystals are sometimes deposited in glass by heat treatment. For most glass materials, microcrystals are deposited on the glass surface in large amounts and the distribution thereof is nonuniform, so that cracks are liable to be generated, by which the apparent strength of glass material is decreased. In particular, in the method for manufacturing the above-described magnetic head for high-density recording, the back sealing glass is heated two times, so that crystals are liable to be deposited in the glass. Nonuniform deposition of crystals in the sealing glass decreases the strength thereof. Therefore, when the core having been made in unit form after sealing is cut and ground, cracks develop in the joint portion.
The glass material referred to as so-called crystallized glass is a material whose apparent strength is increased by the uniform deposition of microcrystals in the whole glass by means of heat treatment, different from the crystallization of many glass materials. However, because the composition of crystallized glass is limited, it is difficult to obtain a material having desired physical properties. Also, because the heat treatment conditions during use are limited, the material cannot be used practically in many cases. The sealing glass used for the magnetic head is required to meet many conditions including working point, coefficient of thermal expansion, chemical durability, or the like suitable for the specifications of the magnetic head. Therefore, it is desirable to select amorphous glass that has a high degree of freedom of composition and is less prone to be crystallized.
Therefore, the above-described sealing glass for magnetic head preferably has a high strength caused by the fact that it is not crystallized under the heating condition in the magnetic head manufacturing process, in addition to having the optimum working point and coefficient of thermal expansion.
However, the sealing glass having a composition proposed in Japanese Patent Application Laid-Open Nos. 7-161011 and 8-180310 has not been developed considering the problems of crystallization and strength. Therefore, when the magnetic head is manufactured by the manufacturing method that realizes the above-described high-density recording, since the strength of the front and back sealing glasses is insufficient, cracks are generated, and sometimes cracking and chipping are caused in the magnetic head.
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to provide a high-performance magnetic head in which cracks in sealing glass and cracking and chipping of head are less prone to occur even when the magnetic head is manufactured because the glass is not crystallized and therefore the chip strength of head can be increased.
To attain the above object, the present invention provides a front sealing glass and back sealing glass for magnetic head.
The front sealing glass has a chemical composition of 13 to 17 wt % SiO2, 5 to 6.8 wt % B2O3, 70 to 77 wt % PbO, 0.1 to 5 wt % of at least one of Al2O3 and ZnO, and 0.1 to 3 wt % of at least one of Na2O and K2O on an oxide basis, and preferably has a composition of 16 to 17 wt % SiO2, 5 to 6.8 wt % B2O3, 75.5 to 77 wt % PbO, 0.1 to 5 wt % of at least one of Al2O3 and ZnO, and 0.1 to 3 wt % of at least one of Na2O and K2O on an oxide basis.
The back sealing glass has a chemical composition of 3 to 9 wt % SiO2, 11 to 17 wt % B2O3, 66 to 77 wt % PbO, and 3 to 15 wt % of at least one of Al2O3 and ZnO on an oxide basis, and preferably has a composition of 3 to 9 wt % SiO2, 11 to 17 wt % B2O3, 68 to 77 wt % PbO, 4 to 14 wt % of at least one of Al2O3 and ZnO on an oxide basis.
Further, the present invention provides a high-performance magnetic head in which a pair of magnetic core halves, in which a coil groove is provided at least on one side, and a metallic ferromagnetic film is formed on at least one gap facing surface, are joined by butting the gap facing surfaces together via a magnetic gap meterial, joining the front gap side by using the front sealing glass, and joining the back gap side by using the back sealing glass.